In recent years, a demand for a disc-type coil having a conductor pattern formed thereon by etching or press work is increasing because of a tendency of reduction in thickness of various devices. However, the disc-type coil has an inconvenience that a value of a current flowing through a coil obtained by winding a wire rod is reduced since there is a limit in a wiring amount of a conductor pattern. Therefore, there is an attempt to increase the wiring amount of the conductor pattern by laminating the disc-type coils and connecting them in series. For example, there has been suggested a coil apparatus having a configuration that many lamination through holes are radially provided in an inner circumferential portion of an insulating substrate of a disc-type coil, a leading end and a terminating end of a conductor pattern are connected to two through holes, which are common to each disc-type coil, in many lamination through holes, and each lower disc-type coil below the uppermost disc-type coil is thereby rotated in accordance with an angle of arrangement of the lamination through holes and then laminated (Patent Literature 1). Each of the plurality of laminated disc-type coils is rotated in accordance with the angle of the arrangement of the lamination through holes in each disc-type coil to effect positioning of the lamination through holes, and then the lamination through holes are soldered to connect the disc-type coils.
In the disc-type coil are provided two types of through holes, i.e., through holes that are arranged on the outer circumferential side of each conductor pattern and connect the conductor patterns on both surfaces to each other and a pair of through holes that are arranged on the inner circumferential side of each conductor pattern and connected to the conductor pattern on the front side and the conductor pattern on the back side to function as a leading end and a terminating end. Further, for example, four disc-type coils of this kind are laminated, a pair of through holes serving as a leading end and a terminating end on the inner circumferential side of the conductor pattern are arranged at an interval of an angle of 36°, and three pairs of through holes, each pair of which serve as a leading end and a terminating end, are arranged on the same circumference at intervals of an angle of 81°. Furthermore, a lower disc-type coil is in phase with an upper disc-type coil at an angle of 81° and sequentially laminated, and through holes serving as a leading end and a terminating end on each disc are soldered as lamination through holes, whereby the conductor patterns of the four laminated disc-type coils form a coil of one independent circuit, thus forming a coil with a long wire length.